Mobile communication devices include a receiver configured to receive an incoming signal. However, a direct current (DC) offset is frequently present in the signal at various stages in a receiver design. The DC offset may cause inefficient operation of the receiver or, in extreme cases, may prevent the receiver from operating at all.
To avoid the problems that may be caused by DC offset, a correction or cancellation process is generally used to remove the unwanted DC component while preserving the fidelity of the higher frequency components of the signal. Since an ideal filter (i.e., one that can remove the DC component while perfectly preserving the other frequency components) is not practical or even possible to implement, receiver designs typically include a high pass filter having a fixed cutoff frequency. The cutoff frequency may be chosen as a compromise between various requirements, including fast convergence of initial DC offset correction upon activation of the receiver (requires higher 3 dB cutoff frequency), the preservation of the fidelity of the received signal during receiver operation (requires lower 3 dB cutoff frequency), and the ability to track anticipated subsequent changes in the nature of the unwanted DC component throughout the operation of the receiver (requires varying 3 dB cutoff frequencies depending on DC levels).
However, balancing the various requirements is difficult because some of the requirements conflict with others. For example, relatively large fluctuations in DC levels generally require a high cutoff frequency response, but this requirement is at odds with the requirement to preserve the received signal fidelity. Accordingly, improvements are needed in correcting DC offsets in wireless receivers to address such difficulties.